[FIX] use existing field value of nick_name in db if not sent during request

[Chethan-rao]

When a card is saved with nick_name during 1st time, if the same card is being saved next time with no nick_name, the nick_name field is being null. This is because we are only relying on request's nick_name field. We should first infer the value from the request. If not present/sent in request, we fallback to the existing field value in db.